MicroRNA-33a deficiency inhibits proliferation and fibrosis through inactivation of TGF-β/Smad pathway in human cardiac fibroblasts

Cardiac fibroblasts (CFBs) play pivotal roles in myocardial fibrosis, which is the leading cause of arrhythmia. This study was aimed to investigate the modulation of microRNA (miR)-33a on proliferation, apoptosis and fibrosis of human CFBs. CFBs were respectively transfected with miR-control, miR-33a mimic or miR-33a inhibitor, followed by induction of transforming growth factor-β (TGF-β). Non-treated CFBs acted as control. Cell viability, apoptosis, and fibrosis which reflected by expressions of Col-I, Col-III and α-smooth muscle actin (α-SMA) were evaluated by CCK-8 assay, flow cytometry, qRT-PCR and Western blot analysis. Finally, key kinases involved in the TGF-β/Smad pathway were evaluated by Western blot analysis. TGF-β enhanced CFB viability, and expression levels of Col-I, Col-III and α-SMA in CFBs (P < 0.01 or P < 0.001). The increased CFB proliferation, and upregulation of Col-I, Col-III and α-SMA were all further enhanced by miR-33a mimic (P < 0.05 or P < 0.001), whereas reversed by miR-33a inhibitor (P < 0.05, P < 0.01 or P < 0.001). The CFB apoptosis was remarkably promoted by miR-33a inhibitor (P < 0.001). Results of signaling pathway showed that phosphorylated levels of Smad-2 and Smad-3 were both upregulated by TGF-β (P < 0.001). The upregulated phosphorylations were further improved by miR-33 mimic (P < 0.05) while reversed by miR-33a inhibitor (P < 0.05 or P < 0.001). miR-33a deficiency inhibits proliferation and fibrosis of CFBs while promotes CFB apoptosis by inactivation of TGF-β/Smad pathway.